Extrapolation of Test Performance for Air-to-Air Rotary Energy Exchangers
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Abstract
Air-to-air energy exchangers are used in building HVAC systems to transfer energy between the exhaust air and the outdoor air. Because of its potential to reduce the energy consumption for conditioning ventilation air and to downsize the cooling and heating equipment, air-to-air energy recovery is required for use in many situations according to the prevalent energy efficiency standards (e.g., ASHRAE Standard 90.1) for commercial buildings. Typically, the performance of air-to-air energy exchangers is tested, rated and certified according to industry-accepted standards and procedures such as ASHRAE Standard 84 and AHRI Standard 1060. Because of the expenses and facility constraints associated with laboratory testing, performance rating tests of air-to-air energy exchangers are usually performed at a limited set of standard test conditions for selected products. However, manufacturers may produce a large variety of products with different sizes and energy exchangers may operate in the field under operating conditions different from those in the rating tests. There is a need to extrapolate the test results from small energy exchangers to large ones and from one operating condition to another. This research uses laboratory tests to validate the current extrapolation approach used by AHRI Standard 1060 and the performance correlation equation proposed in literature.Two sets of air-to-air energy wheels from different manufacturers were selected for laboratory testing. Each set included three wheels of different sizes (i.e., small, medium, and large). The tests were performed at the AHRI-certified energy recovery testing facility at Intertek. Each set of wheels had a total 19 laboratory tests covering different test conditions for effectiveness, leakage performance and pressure drop. The analysis of test results showed an overlap in performance ratings between different wheel sizes after accounting for allowable allowances, which in return supported the use of AHRI’s extrapolation approach for performance rating. In addition, the test results were used to validate the selected effectiveness correlations from the literature. It was found that the latent effectiveness correlation matched well with the test results, but a modification of the sensible effectiveness correlation was necessary to match well with the test results. A customized model was developed in EnergyPlus to investigate the impact of operating conditions on annual energy simulation. The simulation of a standalone retail building in Atlanta, GA showed that ignoring the impact of operating conditions on exchanger effectiveness had a negligible impact on cooling energy consumption, but had 5%-18% more heating energy consumption than the model that considered the impact of operating conditions on exchanger effectiveness.